Biological relevance of ZNF224 expression in chronic lymphocytic leukemia and its implication IN NF-kB pathway regulation

Chronic lymphocytic leukemia (CLL) is a heterogeneous disease, whose presentation and clinical course are highly variable. Identification of novel prognostic factors may contribute to improving the CLL classification and providing indications for treatment options. The zinc finger protein ZNF224 plays a key role in cell transformation, through the control of apoptotic and survival pathways. In this study, we evaluated the potential application of ZNF224 as a novel marker of CLL progression and therapy responsiveness. To this aim, we analyzed ZNF224 expression levels in B lymphocytes from CLL patients at different stages of the disease and in patients showing different treatment outcomes. The expression of ZNF224 was significantly increased in disease progression and dramatically decreased in patients in complete remission after chemotherapy. Gene expression correlation analysis performed on datasets of CLL patients revealed that ZNF224 expression was well correlated with that of some prognostic and predictive markers. Moreover, bioinformatic analysis coupled ZNF224 to NF-κB pathway, and experimental data demonstrated that RNA interference of ZNF224 reduced the activity of the NF-κB survival pathway in CLL cells. Consistently with a pro-survival role, ZNF224 knockdown raised spontaneous and drug-induced apoptosis and inhibited the proliferation of peripheral blood mononuclear cells from CLL patients. Our findings provide evidence for the involvement of ZNF224 in the survival of CLL cells via NF-κB pathway modulation, and also suggest ZNF224 as a prognostic and predictive molecular marker of CLL disease.

KRAB-ZFP Transcriptional Regulators Acting as Oncogenes and Tumor Suppressors: An Overview

Krüppel-associated box zinc finger proteins (KRAB-ZFPs) constitute the largest family of transcriptional factors exerting co-repressor functions in mammalian cells. In general, KRAB-ZFPs have a dual structure. They may bind to specific DNA sequences via zinc finger motifs and recruit a repressive complex through the KRAB domain. Such a complex mediates histone deacetylation, trimethylation of histone 3 at lysine 9 (H3K9me3), and subsequent heterochromatization. Nevertheless, apart from their repressive role, KRAB-ZFPs may also co-activate gene transcription, likely through interaction with other factors implicated in transcriptional control. KRAB-ZFPs play essential roles in various biological processes, including development, imprinting, retroelement silencing, and carcinogenesis. Cancer cells possess multiple genomic, epigenomic, and transcriptomic aberrations. A growing number of data indicates that the expression of many KRAB-ZFPs is altered in several tumor types, in which they may act as oncogenes or tumor suppressors. Hereby, we review the available literature describing the oncogenic and suppressive roles of various KRAB-ZFPs in cancer. We focused on their association with the clinicopathological features and treatment response, as well as their influence on the cancer cell phenotype. Moreover, we summarized the identified upstream and downstream molecular mechanisms that may govern the functioning of KRAB-ZFPs in a cancer setting.

ZNF224 is a transcriptional repressor of AXL in chronic myeloid leukemia cells

ZNF224 is a KRAB-zinc finger transcription factor that exerts a key tumor suppressive role in chronic myelogenous leukemia. In this study, we identify the receptor tyrosine kinase Axl as a novel target of ZNF224 transcriptional repression activity. Axl overexpression is found in many types of cancer and is frequently associated with drug resistance. Interestingly, we also found that sensitivity to imatinib can be partly restored in imatinib-resistant chronic myelogenous leukemia cells by ZNF224 overexpression and the resulting suppression of Axl expression. These results, in accordance with our previous findings, support the role of ZNF224 in imatinib responsiveness and shed new insights into potential therapeutic use of ZNF224 in imatinib-resistant chronic myelogenous leukemia.

ZNF224, Krüppel like zinc finger protein, induces cell growth and apoptosis-resistance by down-regulation of p21 and p53 via miR-663a

ZNF224 is a Krüppel-associated box-containing zinc-finger protein which represses gene transcription by interacting with various co-repressors. However, its consensus DNA sequences and target genes are not fully identified. In this study, we identified and characterized consensus DNA sequences containing 5′-CAGC-3′; recognized by ZNF224 through ChIP-sequencing, which further confirmed by ELISA, SPR, qPCR, and luciferase activity assay. ZNF224 increased miR-663a transcription by binding to miR-663a promoter, which in turn binds to 3′; UTR of p53 and p21 to decrease their expression. miR-663a antagonist abolished ZNF224-mediated suppression of p21 and p53, resulting in the enhanced apoptosis by CPT. The analyses using human breast ductal carcinoma tissues exhibited that the expression of ZNF224 and miR-663a was increased in cancer compared to non-cancer region. Consequently, ZNF224 increases cell survival and decreases apoptosis by decreasing the expression of p53 and p21 via miR-663a as a transcriptional activator. Taken together, we identified and characterized DNA binding element of ZNF224, and its target genes, miR-663a, which provides a novel insight in the down-regulation of p21 and p53 via miR-663a by ZNF224 in breast cancer.

Role of ZNF224 in c-Myc repression and imatinib responsiveness in chronic myeloid leukemia

The transcription factor ZNF224 plays a key proapoptotic role in chronic myelogenous leukemia (CML), by modulating Wilms Tumor protein 1 (WT1) dependent apoptotic genes transcription. Recently, we demonstrated that Bcr-Abl signaling represses ZNF224 expression in Bcr-Abl positive CML cell lines and in CML patients. Interestingly, Imatinib and second-generation tyrosine kinase inhibitors specifically increase ZNF224 expression.

On the other hand, Bcr-Abl positively modulates, via JAK2 activation, the expression of the c-Myc oncogene, which is required for Bcr-Abl oncogenic transformation in CML. Consequently, JAK2 inhibitors represent promising molecular therapeutic tools in CML.

In this work, we demonstrate that ZNF224 is a novel transcriptional repressor of c-Myc in CML. We also show that ZNF224 induction by Imatinib and AG490, a specific JAK2 inhibitor, is responsible for the transcriptional repression of c-MYC, thus highlighting the crucial role of the ZNF224/c-Myc axis in Imatinib responsiveness.

Interestingly, we also report that ZNF224 is induced by AG490 in Imatinib-resistant CML cells, leading to c-Myc repression and apoptosis induction. These findings suggest that the development of molecular tools able to induce ZNF224 expression could provide promising means to bypass Imatinib resistance in CML.

The Complex Role of the ZNF224 Transcription Factor in Cancer

ZNF224 is a member of the Kruppel-associated box zinc finger proteins (KRAB-ZFPs) family. It was originally identified as a transcriptional repressor involved in gene-specific silencing through the recruitment of the corepressor KAP1, chromatin-modifying activities, and the arginine methyltransferase PRMT5 on the promoter of its target genes. Recent findings indicate that ZNF224 can behave both as a tumor suppressor or an oncogene in different human cancers. The transcriptional regulatory properties of ZNF224 in these systems appear to be complex and influenced by specific sets of interactors. ZNF224 can also act as a transcription cofactor for other DNA-binding proteins. A role for ZNF224 in transcriptional activation has also emerged. Here, we review the state of the literature supporting both roles of ZNF224 in cancer. We also examine the functional activity of ZNF224 as a transcription factor and the influence of protein partners on its dual behavior. Increasing information on the mechanism through which ZNF224 can operate could lead to the identification of agents capable of modulating ZNF224 function, thus potentially paving the way to new therapeutic strategies for treatment of cancer.

WT1-mediated repression of the proapoptotic transcription factor ZNF224 is triggered by the BCR-ABL oncogene

The Kruppel-like protein ZNF224 is a co-factor of the Wilms’ tumor 1 protein, WT1. We have previously shown that ZNF224 exerts a specific proapoptotic role in chronic myelogenous leukemia (CML) K562 cells and contributes to cytosine arabinoside-induced apoptosis, by modulating WT1-dependent transcription of apoptotic genes. Here we demonstrate that ZNF224 gene expression is down-regulated both in BCR-ABL positive cell lines and in primary CML samples and is restored after imatinib and second generation tyrosine kinase inhibitors treatment. We also show that WT1, whose expression is positively regulated by BCR-ABL, represses transcription of the ZNF224 gene. Finally, we report that ZNF224 is significantly down-regulated in patients with BCR-ABL positive chronic phase-CML showing poor response or resistance to imatinib treatment as compared to high-responder patients. Taken as a whole, our data disclose a novel pathway activated by BCR-ABL that leads to inhibition of apoptosis through the ZNF224 repression. ZNF224 could thus represent a novel promising therapeutic target in CML.

The hematopoietic tumor suppressor interferon regulatory factor 8 (IRF8) is upregulated by the antimetabolite cytarabine in leukemic cells involving the zinc finger protein ZNF224, acting as a cofactor of the Wilms' tumor gene 1 (WT1) protein

The transcription factor interferon regulatory factor-8 (IRF8) is highly expressed in myeloid progenitors, while most myeloid leukemias show low or absent expression. Loss of IRF8 in mice leads to a myeloproliferative disorder, indicating a tumor-suppressive role of IRF8. The Wilms tumor gene 1 (WT1) protein represses the IRF8-promoter. The zinc finger protein ZNF224 can act as a transcriptional co-factor of WT1 and potentiate the cytotoxic response to the cytostatic drug cytarabine. We hypothesized that cytarabine upregulates IRF8 and that transcriptional control of IRF8 involves WT1 and ZNF224. Treatment of leukemic K562 cells with cytarabine upregulated IRF8 protein and mRNA, which was correlated to increased expression of ZNF224. Knock down of ZNF224 with shRNA suppressed both basal and cytarabine-induced IRF8 expression. While ZNF224 alone did not affect IRF8 promoter activity, ZNF224 partially reversed the suppressive effect of WT1 on the IRF8 promoter, as judged by luciferase reporter experiments. Coprecipitation revealed nuclear binding of WT1 and ZNF224, and by chromatin immunoprecipitation (ChIP) experiments it was demonstrated that WT1 recruits ZNF224 to the IRF8 promoter. We conclude that cytarabine-induced upregulation of the IRF8 in leukemic cells involves increased levels of ZNF224, which can counteract the repressive activity of WT1 on the IRF8-promoter.